Engineering Pro-Osteogenic Poly(l-Lactide-co-ε-caprolactone) Sponges Through Carbonate Apatite Integration

Flexible and porous sponges with high osteoconductivity have a wide range of bone healing applications. Although polymer/ceramic composite materials can serve as soft bone grafts, osteogenesis can be compromised when the ceramic surface is covered by the polymer. This study aimed to fabricate a bone-graft sponge with high elasticity and osteoconductivity by integrating carbonate apatite (CAp) particles inside and on the surface of poly(l-lactide-co-ε-caprolactone) (PLCL). A slurry comprising PLCL and a calcium carbonate (CaCO₃) precursor was freeze-dried to obtain a PLCL/CaCO₃ sponge, which was then phosphatized into a PLCL/CAp sponge using a mildly alkaline sodium phosphate solution. This sodium phosphate solution not only converted CaCO₃ into CAp but also partially degraded the PLCL matrix to expose CAp on the surface, which improved the hydrophilicity of the surface. Interconnected macropores with diameters of 500-600 μm were also introduced by embedding and subsequently leaching sodium chloride (NaCl) crystals from the PLCL/CaCO₃ sponge. In vitro cell experiments demonstrated that CAp and the macroporous structure significantly enhanced osteoblast adhesion and differentiation. In vivo evaluations using a rabbit femoral defect model revealed that CAp endowed the PLCL sponge with osteoconductivity, facilitating bone ingrowth from the defect margins in 4 weeks. The macroporous structure enabled bone regeneration throughout the sponge. These findings suggest that the developed PLCL/CAp sponge is a promising biomaterial for bone regenerative applications.